[fix] Don't waste time on dir/file attributes in subdirs (#5819)
[fix] Don't waste time on dir/file attributes in subdirs (#5819)

An awful lot of effort was wasted getting attributes just for getting a count of the number of files/directories in subdirectories. Getting the count is pretty fast. Getting all the attributes is not, and in this context we don't even use the attributes.

See <https://www.mobileread.com/forums/showthread.php?t=327085> and <https://gitter.im/koreader/koreader?at=5e3ac3b9e8a838355918ba13> for discussion.
NiLuJe/koreader,poire-z/koreader,pazos/koreader,mihailim/koreader,NiLuJe/koreader,Hzj-jie/koreader,mwoz123/koreader,poire-z/koreader,koreader/koreader,Markismus/koreader,Frenzie/koreader,koreader/koreader,Frenzie/koreader